Finding the Fourth Proportional to 1,139.40, 1,572.38 and 642.02

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.40 : 1,572.38 = 642.02 : x
2. Step 2: Convert to fraction form
   1,139.40/1,572.38 = 642.02/x
3. Step 3: Cross multiply
   1,139.40x = 1,572.38 × 642.02
4. Step 4: Simplify right side
   1,139.40x = 1,009,499.41
5. Step 5: Solve for x
   x = 1,009,499.41/1,139.40
6. Step 6: Final answer
   x = 885.99